Alarm apparatus



g 1965 c5. K. THOMPSON 3,267,450

ALARM APPARATUS Filed Jan. 6, 1964 CODE TEETH REPEAT EACH 360 3 I M 0 360 1440 2|60 M2 \r o M4 239 244 48 INVENTOR- FIE 2 A7 TOP/115V 3,267,450 lee Patented August 16, 1966 3,267,450 ALARM AHPARATU Glenn K. Thompson, Coon Rapids, Minm, assignor to Honeywell inc, a corporation of Delaware Filed Jan. 6, 196 Ser. No. 335,895 5 Claims. (Cl. 340-213) This invention relates generally to the field of fire alarm systems and more specifically relates to an improved means for detecting and transmitting trouble and alarm conditions in a self-supervised fire alarm system.

The design of fire alarm systems today is dictated to a large extent by the code requirements promulgated by various governmental units and private testing organizations. The codes establish minimum standards. Beyond this, the manufacturer is free to improve his design to achieve the simplicity and reliability necessary to market a system successfully in a highly competitive field. Changes in design which will either maintain or improve a certain standard of performance while at the same time reducing cost of manufacture are eagerly sought.

Codes normally require that a fire alarm system include means to signal the presence of a fault in the system. A typical fire detection circuit includes a source of power; a pair of conductors extending from the source to the remote area to be monitored; a terminating resistance con nected to the conductors in the remote area; and a plurality of normally open condition-operated switches connected in parallel with the terminating resistance. Under normal conditions, a supervisory current flows through the circuit. A trouble relay is connected in series with the circuit for energization by the normal supervisory current. It the fire detection circuit is broken, the trouble relay will de-energize to signal the fact.

Upon the occurrence of a fire, one of the switches will close to short out the termination resistance. The result is an increase in current flow in the circuit. An alarm relay is connected in series with the circuit to detect the sudden increase in current fiow. The alarm relay is selected such that it will remain deenergized under normal supervisory current fiow but will be immediately energized upon the increase in current flow caused by the closure of a condition operated switch. A holding circuit is provided to connect the alarm relay directly to the source once it becomes energized.

In the early days, most fire alarm systems were operated on direct current because of the difiiculty in finding available sources of A.C. and in finding good quality A.C. equipment. Today, however, the vast majority of fire alarm systems utilize A.C. The system disclosed herein was designed to operate directly from a standard 120 volt A.C. source.

Many codes require that the alarm relay coil be supervised. This means that the alarm relay coil and the trouble relay coil must be connected in series in order that the supervisory current pass through the alarm relay coil. If the alarm relay coil were connected in parallel with the trouble relay coil, the system would operate properly on both trouble and alarm, but the alarm relay coil would not be supervised.

Connecting the two relay coils in series in the circuit gives rise to problems in design. During supervisory conditions, the current flow in the alarm circuit is maintained at a low level through the use of a large termination resistance. At this point it is no problem to select a trouble relay which will always be energized under supervisory conditions and an alarm relay which will never be energized by the supervisory current fiow.

When an alarm occurs, however, the termination resistance is shorted out by the condition operated switch to place the full voltage across the alarm line with the two relay coils in series. Since the termination resistance is larger than the impedance in the remainder of the circuit, a large increase in current flow occurs.

At this point, it should be pointed out that the alarm relay coil is rated at 120 volts. This is required since after the alarm relay is energized, a holding circuit is set up which applies the full 120 volts to the coil.

When the initial alarm condition occurs, the full 120 volts is dropped across the alarm line including the condition operated switch, the trouble relay coil and the alarm relay coil. If the coils offered equal impedance to the current flow, the voltage drop would be equal across each coil. With less than 60 volts applied, the alarm relay would not energize. It is therefore imperative that a large percentage of the voltage be dropped across the alarm relay coil to insure energization.

In this system the trouble relay coil is necessarily rated at a comparatively low voltage (6 volts) so that it will energize under supervisory conditions. If, however, the trouble relay coil is simply connected in series with the alarm relay coil, there is a strong possibility that the volttage drop across the alarm relay coil will not be sufficiently large when the termination impedance is shorted out. Many codes require that the alarm relay operate reliably at of the rated voltage measured at the source, in this case 102 volts. Conventional mass pro duced A.C. relays generally do not operate reliably below 80% of rated voltage, in this case 96 volts. If, therefore, the combined voltage drop across the alarm line and trouble relay is large enough to reduce the drop across the alarm relay below 96 volts, its operation will be unreliable. Assuming that the voltage source should drop to 102 volts, only 6 volts can be dropped across the alarm line and trouble relay coil if the 96 volt drop across the alarm relay coil is to be maintained.

The large voltage drop across the alarm relay during alarm conditions as compared to the voltage drop across the trouble relay is obtained to a large extent merely from the different impedance characteristics of a volt relay as compared to a 6 volt relay. This difference, however, is not large enough to insure reliable operation where standard relays are used.

One solution to the problem is to use an alarm relay which will operate at 60 or 70% of the rated voltage. This solution is undesirable in that such relays are specialty items and are therefore almost prohibitively expensive.

A more practical and unique solution to the problem is provided herein by incorporating into the circuit a full wave rectifier bridge to supply current to the trouble relay.

. The input terminals to the bridge are connected in series With the alarm relay coil in the fire detection circuit. The trouble relay coil is connected to the output terminals. The flow of A.C. in the circuit continued since the rectifier bridge offers an insignificant amount of impedance to current flow in either direction. The current flow through the trouble relay coil is undirectional because of the full wave rectification occurring in the bridge. The efiect of so connecting the trouble relay is to reduce considerably the impedance introduced into the circuit by the trouble relay.

The impedance of the trouble relay coil in an A.C. circuit includes both D.C. resistance and inductive reactance. Where D.C. only is applied to the coil, no reactance is present since the magnetic lines of force are not con tinually expanding and collapsing to induce an opposing voltage. By so removing the reactance effects of the coil, only the DC. resistance of the coil is included in the fire detection circuit. This D.C. resistance may well be less than one-half of the impedance that would be introduced into the circuit if the coil were directly connected. The result is an increase in the voltage drop across the alarm relay to thereby increase its reliability of operation.

Since the concept of utilizing a full wave rectifier bridge to eliminate the impedance efiects of the trouble relay coil could be utilized in many alarm circuit applications, it has been incorporated into two typical fire alarm systems in the drawing accompanying this application. It is first utilized in an automatic fire alarm transmitter and secondly it is utilized in a central panel. The central panel includes a trouble relay and an alarm relay which are connected in a loop circuit which extends through the areas to be protected and terminates in an end of line resistor. In each of the areas to be protected, an automatic coded fire alarm transmitter is mounted. Each fire alarm transmitter has its own alarm loop which includes conditicn operated switches. Upon the occurrence of a fire or upon the detection of a trouble in the circuit, the transmitter initiates operation of a coding mechanism, a part of which is included in the alarm loop from the central panel. If a fire occurs, a first coding switch and a normally open switch of the alarm relay which are connected in series across the central pan'el alarm loop send back a coded signal to the central panel. If on the other hand, a trouble condition occurs in the transmitter, the coding motor is again energized to pulse a coding contact which is connected in series with the central panel alarm loop. Thus the signal received at the central panel during fire alarm conditions is separate and distinct from that signal received during a trouble condition at the transmitter. The coded signal received at the central panel will indicate immediately which transmitter is energized and whether the signal is caused by a fire or by a trouble condition.

A primary object of my invention is to improve the reliability of a fire alarm system in which the trouble relay is connected in series with an alarm relay for purposes of supervising the alarm relay, by providing means for reducing the impedance which is introduced into the alarm circuit by the trouble relay.

A further object of the present invention is to reduce the impedance effects of a trouble relay coil in an alarm circuit by connecting the relay coil into the circuit through a full wave rectifier bridge.

Another object of my invention is to increase the voltage drop available for the alarm relay coil in a fire alarm circuit by providing means to decrease the impedance of other AG. operated devices within the circuit.

A further object of my invention is to provide a supervised fire alarm system having a distinctive alarm and trouble sequence indicative of the status of the system.

Other objects of this invention will become apparent from the specification and claims when considered in connection with the accompanying drawing in which:

FIGURE 1 is a schematic diagram of a fire alarm system utilizing the subject invention in which a remote autornatic coded fire alarm transmitter is connected to a central alarm circuit; and

FIGURE 2 is a graph which discloses the position of each of the code switches during a full cycle of operation.

Referring now to FIGURE 1, there is disclosed a simplified schematic diagram of a central fire alarm panel from which a pair of conductors 11 and 12 extend through the areas to be protected and terminate in an end of line resistor 13. The system as shown in the diagram is in the deenergized state. A switch described as normally open is therefore open when the associated relay coil is deenergized. Connected in series in conductor 11 within panel 10 is an alarm relay coil F, a normally closed test button 14, and the input terminals 16 and 17 of a full-wave rectifier bridge 15. Connected across the output terminals of bridge is a trouble relay coil G. Electrical power is supplied to conductors 11 and 12 from a pair of terminals 18 and 19 which are in turn connected to an appropriate source of alternating current. A trouble indicating circuit 21 which includes in series a normally closed trouble relay switch G1 and an audible trouble alarm 22 is also connected to terminals 18 and 13. An audible fire alarm circuit 23 which includes in series a normally open alarm relay switch F1 and an audible fire alarm device 24 is also connected to terminals 18 and 19.

Located at a remote location is an automatic coded fire alarm transmitter designated generally as 30. The transmitter circuit is disclosed in an across the line type diagram in which the switches are separated from their actuating means. For example, relay coil A operates four separate switches which are labelled as A1, A2, A3, and A4. Line voltage alternating current is supplied to the transmitter through a pair of terminals L1 and N which are connected respectively to conductors 31 and 32 in the transmitter.

A supervised alarm circuit is connected between conductors 3:1 and 32 which includes in series an alarm relay coil A, the input terminals 33 and 34 of a full wave rectifier bridge 36, a normally closed test button 37, a conductor 38 which extends through the area to be protected, an end of line resistor 33, a second conductor 41 extending through the area to be protected, and a panel terminal 42. Connected across the output terminals 43 and 4 4 of bridge 36 is a trouble relay coil T. Connected in parallel with end of line resistor v35! are a pair of normally open condition responsive switches 46 and 47. The operation of the condition responsive switches in the remote area is not dependent upon a source of power from the panel. These switches are operated by independently energized devices or by mechanically operated devices. For example, switch 46 could be operated by a temperature sensitive bimetal which would close the contacts upon a rise in temperature above a predetermined point.

A holding circuit which includes normally open relay switch A1 is connected from terminal 33 to a panel terminal 48. A jumper 49 connects terminal '48 to terminal 42.

An abnormal condition indicating means embodied as a gas discharge tube 55, and a resistor 56, a resistor 57, and a relay coil B are connected in series between conductors 3 1 and 32. Connected in parallel with gas tube 55 and resistor 56 are series connected switches T 1 and E1, both normally open. Connected in parallel with normally open relay switch E1, resistor 57, and relay coil B is a series connected circuit including a relay coil C and a resistor 58.

The transmitter also incorporates a coding mechanism including a code motor 59 which operates through appropriate coding cams a plurality of cam operate-d switches. The code motor itself is a synchronous AC. motor. Cam operated single pole double throw switch M1 includes a movable member 61, a normally closed contact 62 and a normally open contact 63. Switch M2 is a normally open single pole single throw switch. Switch M3 includes two simultaneously operated switches M3a and M317 which are connected into the alarm loop from the central panel. Switch M3a is a normally open single pole single throw switch while switch M312 is a normally closed single pole single throw switch. Switch M4 is a single pole double throw switch which includes a movable member 64, a normally closed contact 66 and a normally open contact 67.

One side of code motor 59 is connected to conductor 32 by a conductor 68. The other terminal of code motor 59 is connected to movable member 61 of switch M1 by a conductor 69. Movable member 61 of switch MI is also connected to conductor 31 by a conductor 71 having in series therein a normally open relay switch D1. Normally closed contact 62 of switch M1 is connected to movable member 64 of switch M4 by a conductor 72 and a conductor 73. Normally closed contact 62 is also connected to conductor 31 by a conductor -72 and a conductor 74 which includes in series a normally open alarm relay contact A3. Normally open contact 63 of switch M1 is connected to normally open contact 67 of switch M4 by a conductor 76 and a conductor 77. Normally open contact 67 is connected to conductor 31 by con- (Motor '77 and a conductor 78 which includes in series a normally closed alarm relay contact A2 and a normally open relay contact C1. Normally close-d contact 66 of switch M4- is connected to conductor 31 by a conductor 79 which includes in series a relay coil E and a resistor 81. Normally closed contact 66 is also connected to a point on conductor 73 between switch A2 and switch 01 by a conductor 82 in which is connected a normally open single pole single throw relay switch C2.

Also connected in series by a conductor 83 between conductors 31 and 32 are a relay coil D and coding switch M2.

An isolated normally open single pole single throw relay .contact H1 is available for external connection through transmitter terminals 84 and 86. An isolated normally closed relay contact B2 is also available for external connection through terminal 84 and a terminal 87.

Normally open coding switch M3a and normally open alarm relay switch A4 are connected in series between conductors 11 and 12 of the central alarm system. Normally closed coding switch M312 is connected in series with conductor '12 at a point electrically further from the main panel than the previously mentioned connections of switches M3a and A4.

In FIGURE 2 a graph which shows the code switch positions during a full cycle of operation of the transmitter is disclosed. The base line for switch M3 in FIG URE 2 represents the normal positions of switches M3a and M31) as disclosed in FIGURE 1. When the code teeth come into play, the two switches pulse simultaneously in a manner determined by the arrangement of the code teeth.

The graph is essentially a linear representation of the circular coding cams which drive the coding switches. The position marked zero degrees on the graph represents the normal position of the cams and switches as disclosed in FIGURE 1. Switch M2, for example, has just dropped into a depression in the coding cam at zero degrees to reach the normally open position shown in FIGURE 1. Switch M4 at zero degrees is in the normally closed position shown in FIGURE 1 and will remain in that position until the coding cam has rotated 58 at which time switch M4 will move to the normally open position adjacent contact 67. Switch M1 is in the normally closed position at zero degrees and will remain in that position until the coding cam rotates approximately 235 at which time switch M1 will move to its opposite position. The full operation of the coding cams will be discussed at a later point in the specification.

OPERATION The operation of this system may be more easily understood if the several phases of operation are considered separately. These phases or conditions include:

(1) Supervisory condition.

(2) Alarm condition caused by the closure of a normally open condition operated switch in the transmitter alarm loop.

(3) Trouble condition caused by a break in the transmitter alarm loop.

(4) Trouble condition caused by a break in the circuit to the code motor.

(5) Trouble condition caused by a break in the central alarm loop.

The system as shown in the diagram is in the deenergized state. The relay switches will therefore reverse their position when the associated relay is energized. The coding switches are in the position designated as zero degrees in FIGURE 2.

(1) Supervisory condition When power is applied to terminals L1 and N of trans mitter 30, a line voltage A.C. potential is available hetween conductors 31 and 32. A first supervisory circuit is established through alarm relay coil A, bridge 36, test switch 37, conductor 38, end of line resistor 39, conductor 41, and terminal 42. The line voltage potential existing between conductors 31 and 32 thus provides a current flow through the first circuit to supervise the alarm loop and alarm relay coil A. Because of the large end of line resistance 39, the voltage drop across alarm relay coil A is not sufficiently large to energize the relay. Trouble relay coil T, however, receives sufficient current flow to energize it. If therefore, the first circuit is broken, trouble relay coil T will be deenergized.

A second circuit, for supervising the code motor, is also established between conductors 31 and 32. This circuit includes conductor 68, code motor 59, conductor 69, switch M1, switch M4, resistor 81, and relay coil E. Be cause of the large resistance of resistor 81, the current flow in the second circuit is insufficient to energize code motor 59 but relay coil E is energized during supervisory conditions.

A third circuit is also established during supervisory conditions to prevent energization of gas discharge tube 55. This circuit includes relay coil B, resistor 57, switch E1 which is now closed, and switch T1 which is also closed. Switches T1 and E1 effectively short out tube 55. Relay coil B is energized by the flow of current in this circuit. Current also flows through resistor 58, relay coil C, and switch T1. Relay coil C is also energized by this current flow.

During supervisory conditions then, relay coils T, B, C, and E are energized. Code motor 59 and alarm relay coil A are both deenergized.

In central panel 10, a source of line voltage alternating current is applied to terminals 18 and 19. A supervisory alternating current thus flows through the central panel alarm loop which includes bridge 15, test switch 14, alarm relay coil F, conductor 11, end of line resistor 13, and conductor 12. Again relay coil F is selected so that it will not be energized under the influence of the supervisory current. Relay coil G which is connected across the output terminals of bridge 15 is subjected to full wave rectified DC. and is selected so that it will be energized under the influence of the supervisory current flow. Audible trouble alarm 22 and fire alarm 24 are both deenergized during supervisory conditions since both switch F1 and switch G1 are open.

(2) Alarm condition caused by the closure of a normally open condition operated switch in the transmitter alarm loop Assume now that a fire occurs in the space monitored by transmitter 30 and that condition operated switch 46 hasclosed its contacts in response to the fire. The closure of switch 46 effectively shorts out end of line resistor 39. The removal of this large resistance from the circuit causes a large increase in current flow and a correspondingly large increase in the voltage drop across alarm relay coil A. Alarm relay coil A is thus immediately energized and a holding circuit is established through switch Al, terminal 48, and jumper 49. Once this holding circuit has been established, condition operated switch 46 may cpol and reopen without affecting the transmission of the a arm.

As soon as coil A energizes, switch A3 closes to provide line voltage through switch M1 to code motor 59. Code motor 59 is thus energized and begins operation of the coding switches in accordance with the pattern set out in FIGURE 2. Within a few degrees of rotation, switch M2 closes to energize relay D. Switch D1 thus closes to provide an alternate source of power to the code motor. At this point switch M2 has closed and switches M1 and M4 have not changed position. Coding switch M3a and M31: are pulsing in accordance with the code teeth pattern. During the first sixty degrees of rotation of the coding cams for switches M1, M2, and M4, the coding cam for switch M3 has made a full 360 rotation. In the preferred embodiment one full round of code is transmitted during the 360 rotation. The response at the central panel is as follows. Switch A4 is closed since relay A is energized. Switch M3a thus shorts out the central panel alarm loop between conductors 11 and 12. This shorting out of end of line resistor 13 causes an in crease in current flow in the circuit to energize relay F. Each time switch M3a closes, relay F is energized to close switch F1 to in turn energize fire alarm 24. Since no holding circuit is established in the central panel, the alarm will pulse in accordance with the pulsing of switch M3a. It is noted that switch M3b also breaks the alarm loop during this time. Since M3a and M3b are synchronized, however, this breaking of the alarm loop at a point electrically further from the central panel than switch M3a and switch A4 does not affect the energization of trouble relay G since there is constant current flow through relay G.

At the end of 58 of rotation of the cam, switch M4 is switched to the open position with movable member 64 in contact with contact 67. Relay E is thus deenergized. Switch M2 opens momentarily at 60 to deenergize relay D. The code motor continues to operate since a circuit is available through M1 and A3.

When relay E deenergizes, switch E1 opens. With E1 open a current path is established through relay B, resistor 57, gas discharge tube 55 and resistor 56. This voltage is sufficient to break down tube 55 to cause it to light. The lighting of tube 55 thus indicates locally that an abnormal condition is present. The opening of switch E1 and the introduction of tube 55 and resistor 56 into the circuit causes relay B to deenergize. The contacts of relay B are isolated from the remainder of the circuit but are accessible through panel terminals 84, 86 and 87. Contacts B1 and B2 can be utilized to provide local audible signals or any other desired type of signal.

The code continues to sound as the cams continue to rotate. When the rotation reaches 235", the sloping cam surfaces begin moving switches M1 and M4 to opposite positions. At 239 switch M1 has been moved to the open position with movable member 61 adjacent contact 63, and switch M4 has been returned to the closed position. Since con-tact M2 is still closed at this point, relay D is energized and the code motor is energized through contact D1. At exactly 240 contact M2 is sharply opened to deenergize relay D, open contact D1 and deenergize the code motor. It is noted at this point that switch M2 is used to stop the motor abruptly rather than to rely upon the movement of switches M1 and M4 up the sloping cam surface to stop the motor. The full return of switches M1 and M4 is thus assured and the stoppage of the motor at exactly 240 is also assured.

When the code motor stops at 240, relay A is energized. Relays B, C, D, E, and T are deenergized. Switches M2, M3a, M 3b, and M4 are in the position shown on the drawing while switch M1 is in the opposite position. The central alarm panel will return to normal supervisory condition but the code motor in the transmitter will remain at 240 until manually reset.

Assuming that condition operated switch 46 has again opened its contacts, the transmitter can be reset to the normal supervisory condition by opening the reset switch in conductor 31. When the reset button is pushed, all power to the panel is lost and all relays are momentarily deenergized. When relay A deenergizes, the holding circuit is broken and when the reset button is again closed, the first circuit including relay A and relay T returns to normal supervisory condition with current flowing through end of line resistor 39. With relay A deenergized, switch A2 closes to provide power to the code motor through switches C1 and M1. The code motor begins to run and immediately closes switch M2 so that power is available to the code motor through switch D1. At 358 switch M1 returns to its normally closed position and at 360 (3) Trouble condition caused by a break in the transmitter alarm loop Assume that during supervisory conditions a break should occur in conductor 38 or that one of the connections to alarm relay coil A should become disconnected. Such a break in the circuit would cause a disruption of the current flow thereby causing the deenergization of relay coil T. With relay T deenergized, switch T1 opens to deenergize relay C. At the same time gas discharge tube is again energized to indicate the presence of an abnormal condition in the system. Relay B is again deenergized to reverse the positions of B1 and B2. With relay C deenergized, switch C closes to set up a circuit for the code motor through switches A 2, 02, M4, and M1. Within a few degrees of rotation switch M2 also closes to energize relay D and close switch D1 to provide another source of power for the code motor. The coding cam for M3 makes a full 360 rotation to send out one round of code. This corresponds to sixty degrees of rotation for the other cams. At switch M4 shifts to the open position and switch M2 opens to break the circuit to the coding motor. The motor thus stops since no power is available.

It should be noted at this point that even a momentary break in the supervisory circuit will result in one full round of code. Once switch M2 has closed, the motor will continue to run until switch M2 is again opened.

Another very important feature is the fact that only the trouble alarm is sounded at the central panel. Since alarm relay A is deenergized, switch A4 is open and the pulsing of coding switch M611 has no effect on the central panel alarm loop. Only the pulsing of coding switch M3b has any effect. The opening and closing of switch M3b causes the simultaneous energization and deenergization of trouble relay G in the central panel to cause operation of trouble alarm 22. Although the same code pattern is sounded, the operator at the central panel can immediately distinguish between a trouble condition and an alarm condition at the remote location. When the trouble in the transmitter is repaired so that power is once again available to the alarm loop, the coding motor will be energized to return the system to the normal supervisory condition. Relay coil T Will be energized by the supervisory current once .again but relay coil A will of course remain deenergized. Switch T1 closes tp energize relay C. When relay C energizes, switch C1 closes to set up a circuit to provide power to the coding motor, the circuit including switch A2, switch 01, switch M4, and switch M1. The motor then runs to 240 where switch M4 returns to the normally closed position and switch M1 moves to the opposite normally open position. The motor then is provided with power through switches M1, 01, and A2. Of course switch M2 is also closed to energize relay D to provide power to the motor through switch D1. At 358 switch M1 returns to its normally closed position and at 360 switch M2 opens to stop the motor. The transmitter is once again in supervisory condition with all switches in the normal supervisory positions. During this resetting of the transmitter from the trouble condition, a trouble alarm is sounded at the central panel.

At 3 60, relay E is again energized to close contact B1. This deenergizes gas discharge tube 55 and causes the energization of relay B.

(4) Trouble condition caused by a break in the circuit to the code motor During normal supervisory conditions the code motor is supervised by a current which flows through conductor 68, code motor 59, conductor 69, switch M1, switch M4, resistor 81, and relay E. If this circuit is disrupted, relay E will deenergize to open switch E1. Once again an abnormal condition will be indicated by the energization of gas discharge tube 55 and the deenergization of relay coil B. This signal will not be sent back to the central panel since the code motor is inoperative but the local alarms will sound. When the circuit is repaired, relay E will again energize to open contact E1, deenergize gas tube 55 and energize relay B. The system is then in normal supervisory condition.

(5) Trouble condition caused by a break in the central alarm loop A signal at the central panel is also available when a break occurs in either of conductors 11 or 12. If such a break occurs, the supervisory current is disrupted to deenergize trouble relay G. Switch G1 then closes to energize trouble alarm 22. Since this alarm is not coded the operator is aware that the defect is in the central alarm system rather than in the remote transmitter.

The above description is complete as far as this embodiment of the fire alarm system is concerned. It is intended of course that a plurality of transmitters identical to transmitter 30 would be utilized with each central panel. Each of the transmitters would be connected into the central alarm loop in the same fashion as indicated here. By utilizing different coding cams the distinction between the transmitters could be maintained. It is also apparent that additional features common to fire alarm systems could be added into the circuit if required by the code or by the purchaser of the system. In some systems it might be desirable to remove the jumper 49 between terminals 42 and 48 on the transmitter. This would allow the transmitter to automatically reset as soon as the condition operated switch would open since the holding circuit would no longer be provided. This is a matter of choice and is dependent upon system requirements.

Thus it can be seen that this system provides a simple, reliable and unique method of monitoring the condition of a plurality of normally open condition responsive switches in a plurality of remote areas. While I have described and illustrated what appears to be the preferred form of the invention, the scope of the invention should only be limited by the appended claims in which I claim:

1. In a self-supervised coded alarm system; the combination, comprising: a source of power; an alarm relay having an alarm relay coil and a plurality of alarm relay switches operated thereby; a rectifier bridge having input and output terminals; first circuit means including an end of line resistor connecting said alarm relay coil and said input terminals in series with said source to provide a normal supervisory alternating current therethrough; at least one normally open condition operated switch connected in parallel with said resistor; a trouble relay having a trouble relay coil and a plurality of trouble relay switches operated thereby; means connecting said trouble relay coil to said output terminals for energization thereof by said supervisory current whereby inductive reactance due to said trouble relay coil is not introduced into said first circuit; a coding motor having a plurality of coding switches operated thereby; a third relay having a coil and a switch operated thereby; second circuit means including impedance means connecting said third relay coil and said coding motor in series with said source to provide a small supervisory current through said motor to energize said third relay; a first alarm relay switch connected in parallel with said third relay coil and said impedance means to energize said coding motor upon the energization of said alarm relay due to an increase in current in said first circuit; central alarm indicating means; circuit means including in series a second alarm relay switch said abnormal condition indicating means to short out said abnormal condition indicating means during normal supervisory conditions; circuit means including switch means responsive to the deenergization of said trouble relay connected in parallel with said third relay coil and said impedance means to energize said coding motor; central trouble indicating means; and circuit means including a second coding switch connecting said trouble indicating means to said source.

2. A self-supervised alarm system designed to provide separate coded trouble and alarm signals at a central location from information received over a pair of wires from a single coding motor at a remote location, comprising: alarm relay means having a coil and a switch operated thereby; a rectifier bridge having input terminals and output terminals; a source of alternating current; an end of line resistor at a remote location; a pair of conductors connecting in series with said source said alarm relay coil and said input terminals at the central location and said end of line resistor at said remote location to provide a supervisory current therethrough; trouble relay means having a coil and a switch operated thereby; means connecting said trouble relay coil to said output terminals for energization by said supervisory current; a coding motor at said remote location having a plurality of coding switches operated thereby; means for operating said coding motor upon the detection at said remote location of an alarm condition; means for operating said coding motor upon the occurrence of a trouble condition at said remote location; a remote alarm relay at said remote location having a coil and a switch operated thereby; means for energizing said remote alarm relay coil during alarm conditions; first circuit means connecting a first coding switch and said remote alarm relay switch in series across said pair of conductors to short out said end of line resistor upon the closing of both of said switches during alarm conditions; a second coding switch operated simultaneously with said first coding switch connected in series with one of said pair of conductors at a point electrically further from said central location than said connections of said first circuit means; trouble indicating means at said central location; means connecting said trouble indicating means and said switch of said trouble relay means in series with said source for energization thereby upon the deenergization of said trouble relay means caused by a predetermined reduction in the level of said supervisory current; alarm indicating means; and means connecting said alarm indicating means and said switch of said alarm relay means in series with said source to energize said alarm indicating means upon the energization of said alarm relay means caused by the closing of both said first coding switch and said remote alarm switch.

3. A self-supervised fire alarm system designed to sound a coded fire alarm upon the detection of a. fire and to sound a coded trouble signal upon the occurrence of trouble in the system, comprising: a first circuit including a pair of wires and a terminating resistance; a source of AC. potential; a central panel adapted to energize said first circuit from said source; fire alarm means in said central panel responsive to a short across said first circuit; trouble signal means in said central panel responsive to the opening of said first circuit; and remote alarm circuit means, comprising; alarm relay means having a coil and first and second switches operated thereby; rectifying means having input terminals and output terminals, second circuit means including impedance means connecting said input terminals and said alarm relay coil in series with said source, at least one condition operated switch connected in parallel with said impedance means,

trouble relay means having a coil and a switch operated thereby, means connecting said trouble relay coil to said output terminals to energize said trouble relay means from said supervisory current, a coding motor having a plurality of coding switches operated thereby, circuit means including said first alarm relay switch for connecting said coding motor to said source upon the energization of said alarm relay means, circuit means including said switch of said trouble relay means for connecting said coding motor to said source upon the deenergization of said trouble relay means, circuit means connecting a first coding switch and said second alarm relay switch in series across said first circuit to initiate operation of said fire alarm means, and a second coding switch connected in series with said first circuit at a point electrically further from said central panel than said connections for said first coding switch and said second alarm relay switch.

4. A self-supervised alarm system designed to monitor a plurality of normally open condition operated switches, comprising: alarm relay means having a coil and a switch operated thereby; a rectifier bridge having input terminals and output terminals; a source of alternating current; first circuit means including a fixed im edance connecting said alarm relay coil and said input terminals in series with said source to provide a supervisory alternating current therethrough; trouble relay means having a coil and a switch operated thereby; means connecting said trouble relay coil to said output terminals for the energization of said coil by said supervisory current; the impedance introduced into said first circuit means by said trouble relay coil thereby being equal to the DC. resistance of said coil; trouble indicating means; means including said switch of said trouble relay means for connecting said trouble indicating means to said source for energization thereby upon a predetermined reduction in the level of said supervisory current; alarm indicating means; at least one normally open condition operated switch connected in parallel with said fixed impedance to short out said impedance upon the closure thereof; and means including said switch of said alarm relay means for connecting said :alarm indicating means to said source to energize said alarm indicating means upon the energization of said alarm relay coil by an increase in the current fiow in said first circuit occasioned by the closure of said condition operated switch.

5'. A self-supervised alarm system designed to monitor a plurality of normally open condition operated switches, comprising: alarm relay means having a coil and a switch operated thereby; a full wave rectifier bridge having input terminals and output terminals; a source of alternating current; first circuits means including a fixed impedance connecting said alarm relay coil and said input terminals in series with said source to provide a supervisory alternating current therethrough; trouble relay means having a coil and a switch operated thereby; means connecting said trouble relay coil to said output terminals for energization by said supervisory current; trouble indicating means; means connecting said trouble indicating means and said switch of said trouble relay means in series with said source for energization thereby upon a predetermined reduction in the level of said supervisory current; alarm indicating means; at least one normally open condition operated switch connected in parallel with said fixed impedance; and means connecting said alarm indicating means and said switch of said alarm relay means in series With said source to energize said alarm indicating means upon the closing of said condition operated switch to increase the current flow in said first circuit and energize said alarm relay means.

References Cited by the Examiner UNITED STATES PATENTS 2,922,147 1/1960 Bredesen. 3,198,236 8/1965 Puech. 3,212,078 10/1965 Shanahan 340-2l3 NEIL C. READ, Primary Examiner.

R. M. ANGUS, Assistant Examiner. 

5. A SELF-SUPERVISED ALARM SYSTEM DESIGNED TO MONITOR A PLURALITY OF NORMALLY OPEN CONDITION OPERATED SWITCHES, COMPRISING: ALARM RELAY MEANS HAVING A COIL AND A SWITCH OPERATED THEREBY; A FULL WAVE RECTIFIER BRIDGE HAVING INPUT TERMINALS AND OUTPUT TERMINALS; A SOURCE OF ALTERNATING CURRENT; FIRST CIRCUITS MEANS INCLUDING A FIXED IMPEDANCE CONNECTING SAID ALARM RELAY COIL AND SAID INPUT TERMINALS IN SERIES WITH SAID SOURCE TO PROVIDE A SUPERVISORY ALTERNATING CURRENT THERETHROUGH; TROUBLE RELAY MEANS HAVING A COIL AND A SWITCH OPERATED THEREBY; MEANS CONNECTING SAID TROUBLE RELAY COIL TO SAID OUTPUT TERMINALS FOR ENERGIZATION BY SAID SUPERVISORY CURRENT; TROUBLE INDICATING MEANS; MEANS CONNECTING SAID TROUBLE INDICATING MEANS AND SAID SWITCH OF SAID TROUBLE RELAY MEANS IN SERIES WITH SAID SOURCE FOR ENERGIZATION THEREBY UPON A PREDETERMINED REDUCTION IN THE LEVEL OF SAID SUPERVISORY CURRENT; ALARM INDICATING MEANS; AT LEAST ONE NORMALLY OPEN CONDITION OPERATED SWITCH CONNECTED IN PARALLEL WITH SAID FIXED IMPEDANCE; AND MEANS CONNECTING SAID ALARM INDICATING MEANS AND SAID SWITCH OF SAID ALARM RELAY MEANS IN SERIES WITH SAID SOURCE TO ENERGIZE SAID ALARM INDICATING MEANS UPON THE CLOSING OF SAID CONDITION OPERATED SWITCH TO INCREASE THE CURRENT FLOW IN SAID FIRST CIRCUIT AND ENERGIZE SAID ALARM RELAY MEANS. 